Sealing arrangement against a moving fabric

ABSTRACT

The invention relates to a sealing arrangement ( 7 ) against a moving fabric ( 4   b ) in a paper machine or the like. The sealing arrangement includes a stiff sealing element ( 9 ) placed on the fabric&#39;s ( 4   b ) side on the entire width in connection with a paper sheet ( 4   a ) supported by the fabric ( 4   b ). The sealing element has been arranged on a support so that the location of the sealing element with respect to the fabric ( 4   b ) can be adjusted nearer to or, correspondingly, further from the fabric. As a sealing element there is at least a single-chambered labyrinth sealing ( 19 ).

This is a national stage of PCT application No. PCT/FI03/000891, filedon Nov. 19, 2003. Priority is claimed on application No. 20022063, filedin Finland on Nov. 19, 2002.

TECHNICAL FIELD OF THE INVENTION

The object of the invention is a sealing arrangement against a movingfabric in a paper machine or the like according to the preamble of theindependent claim presented below. The invention particularly relates toa sealing arrangement including a stiff sealing element placed on theside of the fabric, on the entire width, in connection with a papersheet supported by the fabric.

PRIOR ART

It is known to guide the paper web in different ways in order to keepthe paper sheet to be dried in connection with the wire even at highspeeds of the paper web and at changing speeds. For example, blowapparatuses and arrangements based on the use of underpressure are used.It has been noticed that when the speed of the paper web exceeds 1500m/min, the conventional arrangements are no more sufficient in order tomaintain the functioning stable and undisturbed. It is essential thatthe paper machine functions in a reliable way, i.e. the so-calledrunnability should be good. The time spent on working out web breaksbecomes expensive because at the same time a considerable amount ofproduction is lost. This also affects the reliability of delivery, andthus important economical values of the factory. In order to control airflows and pressure differences it is known to use different kinds ofsealings in connection with the paper web, the wire and the cylinders ofa paper machine. The distance of the sealing from the wire or the paperweb must be accurately guidable: from too big a gap the air may escapein an uncontrolled way, and if the gap is too small, the sealing maytouch the paper web causing damage thereto. The US publication U.S. Pat.No. 6,192,597 presents a structure in which a sealing plate mountedacross the web is used as a sealing element, the location of whichsealing plate can be adjusted with a power cylinder and supported by aswivel nearer to or further from the wire. Because this kind of anarrangement has no self-adjusting properties, the gap needs to besearched by adjusting to a suitable size, which is rather difficult andrequires re-adjusting if the circumstances change. The US publicationU.S. Pat. No. 5,782,009 presents a suction box extending near the paperweb, in which suction box air is sucked from the area close to theopening nip in order to control the paper web. The front edge of thesuction box part is, however, near the paper web and is formed only of asimple plate-like sealing part. The patent application FI 20012160presents a suction box structure in which the so-called Coanda-effect isutilized with the aid of curved sealing elements placed on triggerhinges. The structure is rather large in size filling the interspacebetween the rolls to a great extent. It is also to be taken into accountthat in a mechanical contact the sealing itself wears out even veryquickly due to the effect of the wire. In that case, the sealing needsto be changed every now and then. A worn sealing may even break off,thus causing a severe disruption to production as the wire gets damaged.Production of overpressure air and underpressure air for the use of airguidance systems in the drying section of a paper machine consumes a lotof energy. In order to produce underpressure in a large scale, theelectric motors of the blowers, compressors and underpressure pumps needto have great output capacities and the flow channels belonging to theapparatus need to be big in size. Also the noise problems areconsiderable. Accordingly, the sound attenuators used for noiseprevention are big and expensive and occupy a lot of factory space.

OBJECT AND DESCRIPTION OF THE INVENTION

The main object of the present invention is to reduce or even toeliminate the problems arising in the above-mentioned prior art.

The object of the present invention is especially to improve therunnability and the operating efficiency of a paper machine and thus, atthe same time, the reliability of a paper machine especially when theproduction speed is high, i.e. when the speed exceeds 1500 m/min, even2000 m/min. The object of the invention is also to reduce energyconsumption and noise problems. An object is also to reduce the size ofthe sound attenuators needed for noise prevention.

In order to carry out the above-mentioned objects, among others, thesealing arrangement against a moving fabric in a paper machine or thelike according to the invention is characterized by what is presented inthe characterizing part of the enclosed independent claim.

A sheet in this text means a paper, board or other corresponding sheetthat is manufactured in the paper machine. A fabric means a mesh, a wireor the like, movable in the paper machine in order to support the saidsheet. A labyrinth sealing means all sorts of labyrinth sealingssuitable for the purpose.

The sheet coming from the opening gap between the cylinder and thefabric, such as the wire, supporting the paper web or the like, tends tofollow the more adhesive plain surface of the cylinder with the help ofan underpressure pulse affecting the sheet in the opening wedge space.These forces are counteracted by means of an underpressure through thefabric against the sheet in order to make the sheet follow the fabricahead in the drying section. An object of the invention is to boost andto improve the control of said suctions by reducing the underpressureloss of the underpressure space.

A typical sealing arrangement against a moving fabric according to theinvention in a paper machine or the like comprises a stiff sealingelement placed at least mainly on the entire width of the paper sheet,on the fabric's side, in connection with a paper sheet supported by thefabric. If the sealing element has been arranged on a support so thatthe location of the sealing element with respect to the fabric isadjustable nearer to or, correspondingly, further from the fabric, thenthe functioning of the sealing can be controlled so that the interspacebetween the sealing and the surface to be sealed can be defined, andthus have an effect on the tightness of the sealing arrangement. Thisfact has a considerable influence on the amounts of air needed, and thuson the energy consumption. If at least a single-chambered labyrinthsealing is used as a sealing element, this choice provides a tightersealing than a conventional sealing arrangement, which has a sealingpoint at one place only. Thereby, by the choice of the place of thelabyrinth sealing not only an efficient sealing but also energy savingsare attained.

A labyrinth sealing is particularly advantageous in a sealingarrangement according to the invention in which the sealing element ismovable to different distances from the fabric. If the sealing elementis worn out, for example when getting into contact with the movingfabric due to its own movement, its sealing effect remains considerablygood, thanks to the several sealing points of the labyrinth sealing whencompared to a sealing element having only one sealing point. Thestructure of a labyrinth sealing presents an advantage also when aforeign object, such as a piece of paper, typically damaging thesealing, passes through between the sealing and the fabric. It is thenlikely that at least some of the several successive sealing areas of thelabyrinth sealing remain intact to some extent. To arrange severalsealing points to move simultaneously as in a labyrinth sealing wouldrequire a complicated structure if several separate single sealingelements were used.

One embodiment of the invention comprises means with which the air flowscan be guided so that with the aid of the created air flows the pressureon the fabric side of the sealing element is different than on the otherside of the sealing element. In this way, the sealing element can bemoved, with respect to the fabric, nearer to or further therefrom byguiding said air flows and pressure difference.

Then no special mechanical moving members are needed, but remote controlcan be easily performed by using control engineering known per se.

One embodiment of the invention comprises, in connection with thesealing element, bellows or a corresponding moving element operated witha medium, as well as means for leading the medium into the bellows orthe like in a controlled manner. In this way it is possible to controlthe pressure arranged in the bellows or the like, and thereby themovement of the bellows or the like, and thereby the distance from thefabric of the sealing element connected to said bellows. In this way arelatively simple adjustment of the movement of the sealing element isattained. In the bellows, pressurized air is typically used as apressure medium, even though also other pressure media are possible.

If the nearest surface of the sealing element is, without air flowscaused, at least mainly in a slight contact with the fabric, the sealingeffect is good and, yet, wearing of the sealing is rather small.

According to one embodiment of the invention, the sealing element thatis placed at least mainly on the entire width of the paper web, isformed of at least two, preferably of several successively arrangedsealing element units. Thereby, the arrangement also comprises means fordetachably fixing the individual sealing element units to thearrangement according to the invention, for example to some papermachine frame part located in cross direction. Such sealing elementunits can be separately manufactured and mounted. Thus, the mounting andservicing measures are much more simple and easy than when handling asealing element having the width of the web.

If the sealing element includes a frame structure, which supports a formof sealing that is replaceable in the running position near the surfaceof the fabric, the replacing operation can be performed quickly andeasily. It is advantageous to replace only the easily replaceablesealing element that is worn out.

If the sealing is at least a single labyrinth sealing, preferably amulti labyrinth sealing, an efficient sealing effect and thereby lowenergy consumption are achieved.

According to one embodiment of the invention, a pressure medium is usedfor guiding the location of the sealing element. Thereby, electronic andmechanical structures can be avoided, as such structures often have beenknown to include operational insecurity and malfunctions.

According to one embodiment of the invention, the frame structure of thesealing element includes openings for adjusting the air flow. Suchstructure is simple and secure in operation. Such adjustment openingscan be arranged as combinations, for example in pairs so that theopenings of a pair of openings are in different bodies, which bodies arearranged to be movable in relation to each other. This movement can beguided for example with a medium arrangement according to the inventionso that the openings can face each other entirely or partly, or do notface each other at all. For example, when the openings face each other,an air flow can pass through the openings. When such openings are movedin relation to each other, the air flow through the openings is at leastmainly prevented. In such solutions moving parts may not be necessary atall.

The frame of one sealing element according to the invention is supportedby a hinge-like support element, whereby the structure is easy tomanufacture and has no separate moving parts.

According to one embodiment of the invention, the hinge-like support islocated higher than the sealing element. Then the structure can bearranged so that the gravity of the earth affects the structure with aforce pulling away from the fabric and with the aid of air flows thestructure is deviated from its initial position closer to the fabric.The solution is also safe, as in this case the ending of the deviationtakes the sealing element further away from the fabric, whereby there isno danger of damage. A sealing articulated from below can also beconsidered, but in that case it is usually necessary to secure the lossof load by a mechanical restitution and it is also usually morechallenging to carry out the adjustment of the sealing element'smovement.

A labyrinth sealing arranged in connection with the underpressurizedspace and adjustable by its distance to the fabric is an advantageoussolution, because the manufacture of the sealing element in question canbe carried out with a bigger tolerance and thus with lower costs. Suchan application can however be considered, especially in fairly narrowpaper machines, that the sealing has been carried out otherwisecorrespondingly, but there is whether no adjustment or only a slightmechanical adjustment margin.

It is recommended that the said labyrinth sealing is made of aluminum oralternatively, at least regarding the part that is near the fabric, ofboard, paperboard, polymer or the like. Then the manufacture of thesealing is quite easy and there are several alternative manufacturingmethods for the sealing element made of aluminium, as well as, for therest of the mentioned solutions.

SHORT DESCRIPTION OF THE FIGURES

In the following, the invention is described more closely with referenceto the enclosed schematic drawing, in which

FIG. 1 schematically illustrates an application of the use of theinvention, a part of the drying section of a paper machine, the pocketspace defined by drying cylinders, a turning suction cylinder and awire,

FIG. 2 schematically illustrates the drying section according to FIG. 1enlarged and when using a sealing arrangement according to theinvention,

FIG. 3 schematically illustrates the sealing arrangement enlarged andpartly illustrated in FIG. 2,

FIG. 4 schematically illustrates some possible sealing profiles used inthe sealing space,

FIG. 5 schematically illustrates near the roll one hinged sealingarrangement according to the invention,

FIG. 6 schematically illustrates the lower part of the sealingarrangement according to FIG. 5 when the sealing is far from the paperweb and especially in a replacement position,

FIG. 7 schematically illustrates a sealing arrangement according to FIG.6 in a normal operating position, and

FIG. 8 schematically illustrates a sealing arrangement according to FIG.6 when the sealing element is almost worn out and before replacement.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE FIGURES

In FIG. 1 of the drawing, the reference number 1 refers to a cylinder inthe drying section of a paper machine and the rotation direction of thecylinder 1 is referred to with the reference mark 1 a. A web 4, thatincludes here a paper sheet 4 a marked with a broken line and a fabric 4b marked with an unbroken line, travels after the cylinder 1 to aturning suction roll 2 and further to a cylinder 3. The rotationdirections are marked with arrows 2 a and 3 a. The point of the cylinder1 where the web 4 detaches from the periphery of the cylinder downwardsto the direction of the turning suction roll 2, is marked with thereference number 5 and the reference number 6 is marked at a distancefrom there forward along the web 4.

FIG. 2 illustrates a part of the drying section according to FIG. 1 asan enlargement from the area between the cylinders 1, 2 and 3, and fromthe pocket space formed by the fabric 4 b. Near the points 5 and 6 therehas been placed a sealing arrangement 7 that is formed of a box-likeunderpressure space 8, which has, in the cross direction of the machine,the width of the web 4 or even more if necessary. It is usuallynecessary that the sealing arrangement 7 is located from its upper partat least in some degree higher than the point of the reference number 5,so that the function would be efficient.

FIG. 3 illustrates as an enlargement a sealing element 9 a used at thepoint 6, which sealing element has been placed in suspension from itsupper part to a supporting point 10, which allows the sealing element todecline. It is recommended to use in the supporting point 10 a so-calledtrigger hinge known per se. The sealing element 9 a has a space 11 for alabyrinth sealing or the like, which space 11 is on that side of thesealing element 9 a that is on the fabric's 4 b side of the web 4. Whenpressurized air is led to the box-like part 9 b, this has an effect onthe sealing element 9 a so that the sealing element 9 a moves closer tothe fabric 4 b. The leading of underpressurized or overpressurized aircan take place into the box-like part 9 b at an overpressure via a pipe26 or, alternatively, at an underpressure via openings 27 or via acombination of openings 28 from the underpressure space 8. If theopenings of the combination of openings 28 face each other, an air flowcan pass through this way quite freely, and when the openings of thecombination of openings 28 do not face each other, the flow is a minorleakage flow. The openings 27 can be adjustable, made for example of asliding damper structure (not shown). If the pressure of the pressurizedair is further increased, at a certain point the labyrinth sealing inthe space 11 touches the fabric 4 b, which is disadvantageous becausethen the sealing is quickly worn out. In the supporting point 10 thepivoting has been arranged so as to be rather mobile and therefore ithas been carried out with the help of a so-called knife bearing, triggerhinge or the like, known per se. If, for example, a piece of paper orsome other material foreign to a normal web comes along the web 4, thesealing element 9 a that is very mobile can turn aside, and thereby theprobability of a web break is smaller.

FIG. 4 illustrates some possible sealings, more correctly sealingprofiles that can be used in the sealing space 11. The reference number12 shows a sealing that is conventional as such, having no speciallabyrinth feature at all in addition to what the form of the sealingthat is against the fabric 4 b forms with the fabric 4 b. The sealing 13illustrates a comb-like sealing that has several, preferably more thanten partition walls. The sealing capacity of this kind of a sealing inthe presented application is quite clearly better than that of thesealing 12. A more developed sealing model is shown with the referencenumber 14. Then each sealing brush forms its own sealing point. Thesealing 15 has similar local sealing points as the sealing 14 but thesealing chambers are lower but almost circular in their form, which hasa positive effect on the sealing capacity. All the sealing solutions ofFIG. 4 have a bottom plate from which the sealing is attached to thesealing space 11, most suitably with screws. It is preferred tomanufacture the sealing elements in such a size, that the width in thecross direction of the paper sheet is 40-150 cm, more preferably 70-90cm. Then the manufacturing does not require big working machines andalso the mounting is easier than as a long integral structure. Aluminumis one recommended manufacturing material because it can be extrudedinto a form profile, as well as, machined in rather varied manners intodifferent shapes. The sealings 13-15 resemble the labyrinth sealingsknown per se but the sealings are able to move guided by pressurized airnearer to or further from the fabric 4 b or in case of a malfunctionunder the influence of the material that has come along the web 4. Withthe solution according to the invention the controllability of the papersheet 4 a is good even at rather high web speeds.

In the solution according to FIG. 5 near the drying cylinder 1, therotation direction of which is shown by the arrow 1 a, there is abox-like underpressure space 16 having an upper sealing part 17 and alower sealing part 18. The sealing element 19 is a labyrinth sealinghaving several sealing pockets 20 a-20 d, which are formed between thesealing walls. In FIG. 5 four sealing pockets 20 a-20 d are shown butthe amount of the pockets may vary typically within the limits of 2-10.In this sealing element the pocket interspace is standard. As a sealingframe 21 there is an assembly made of a flexible material, e.g. rubber,to which assembly the sealing walls are attached from their other endsand that are replaceable with new ones at the servicing place. The upperend of the sealing frame 21 has been attached to the grooved slot 22 ofthe box-like part in a flexible and mobile manner. The upper part of thesealing frame below the attachment point but, however, above the topmostsealing pocket 20 d is made of fairly thin rubber that is flexible andbends quite easily, as is shown in FIGS. 7 and 8 later on. In the lowerpart of the sealing frame 21 in touch therewith, there is a bellowselement 23 a or the like, the form and the front part's location ofwhich can be changed by increasing or decreasing the pressure of themedium acting inside the bellows element. In the applications of FIG. 5(not shown) an underpressure of a desired magnitude can be brought intodifferent interspaces of the sealing element in order to reverse theunderpressure produced at the other side, at the point in question bythe opening gap of the opposite side.

In the structure according to FIG. 6 there has been used, in the sealingpart 18, a labyrinth sealing, in the sealing frame 24 of which thelengths of the pockets 25 a-25 d in the direction of the web 4 aredifferent. The other shapes of the sealing element are however similarto those presented in the upper sealing arrangement of FIG. 5. In thecase according to FIG. 6 the overpressure in the bellows 23 b is smallor an underpressure prevails inside it. Thus, the sealing frame 24 isfar from the paper web and the replacing of the sealing frames 24 ispossible by endwise pushing new elements into the slot andsimultaneously they push the old elements away.

In the position illustrated in FIG. 7 the sealing part 18 is in anoperating position, i.e. the front parts of the sealing pockets 25 a-25d are near the fabric 4 b. The pressure of the medium has been increasedin the bellows 23 b when compared to the situation in FIG. 6. Thesealing frame has been bent near the upper part due to the effect of thepressure increase in the bellows 23 b. The advance of the front part ofthe bellows 23 b is usually a few centimeters from one end of the pathof movement to the other, and also the edge parts of the labyrinthpockets are almost of the same length or slightly longer. It is to benoticed that the edge parts of the labyrinth pockets are quite thin sothat they would even bend when at least small so-called paper lumps hitthem or at least no considerable amounts of material would loosen fromthem in these kinds of situations.

In a situation illustrated in FIG. 8 the labyrinth sealing is alreadyrather worn and the path of movement of the bellows 23 b is already atits end. A labyrinth sealing that is this worn needs already to bereplaced.

The fixing structure of the sealing strips formed by the sealing gaps ofthe labyrinth sealing is not shown in the Figures, but it is recommendedthat slots with a so-called dovetail form are formed in the sealingframe 24. Correspondingly, the sealing strips have a form fitting to thedovetail, and thus the strips are pushed in their place at the servicingplace.

Such applications are also advantageous in utilizing the invention, inwhich the above-described sealing element arrangement is part of abigger box of the pocket space, which box maintains the sheet on theouter surface of the fabric with the aid of blow or suction arrangementsor at least with a suction opening, and thus improves the runnability.When integrated to boxes presented e.g. in the patent publications FI106568 and U.S. Pat. No. 5,782,009, the sealing arrangement according tothe invention brings about considerable benefits in the entire pocketarea as with the sealing arrangements a more efficient suction isachieved there, where it is needed as the amount of leaking airdecreases.

The Figures illustrate only examples of preferred applications accordingto the invention. To a person skilled in the art, it is clear that theinvention is not limited only to the above examples, but that theinvention may vary within the frames of the claims presented below. Inthe dependent claims some possible embodiments of the invention arepresented, and they are not to be considered to limit the scope ofprotection of the invention.

1. A sealing arrangement against a moving fabric in a paper machine, thefabric supporting a paper sheet, which sealing arrangement comprises astiff sealing element placed on a side of the fabric that faces awayfrom the paper sheet, the sealing element covering the entire width ofthe fabric and comprising at least one labyrinth seal; a bellowsconfigured for moving the sealing element relative to the fabric;wherein the sealing element is arranged on a support so that a locationof the sealing element with respect to the fabric can be adjusted nearerto or further away from the fabric when the bellows expands orcontracts; and wherein upon depressurization of the bellows such thatthe bellows contracts, the sealing element is adjusted away from thefabric by gravitational forces, and upon pressurization such that thebellows expands, the sealing element becomes adjusted nearer to thefabric by the bellows.
 2. The sealing arrangement of claim 1, whereinthe sealing element comprises successive cross directional sealingelement units.
 3. The sealing arrangement of claim 1, wherein thesealing element further comprises a frame structure, the at least onelabyrinth seal being replaceably supported in a driving position nearthe fabric by the frame structure.
 4. The sealing arrangement of claim3, wherein the at least one labyrinth seal comprises a multi labyrinthseal.
 5. The sealing arrangement of claim 1, wherein a pressure mediumis used to expand or contract the bellows.
 6. The sealing arrangement ofclaim 1, wherein the support comprises a hinge-like support element andthe sealing element is supported, from its frame, on the hinge-likesupport element.
 7. The sealing element of claim 6, wherein thehinge-like support element is located higher than the sealing element.8. The sealing arrangement of claim 1, wherein the at least onelabyrinth seal is made of aluminum board, paper board, or polymer atleast regarding a part thereof that is near the fabric.
 9. The sealingarrangement of claim 2, wherein a pressure medium is used to expand orcontract the bellows.
 10. The sealing arrangement of claim 3, wherein apressure medium is used to expand or contract the bellows.
 11. Thesealing arrangement of claim 4, wherein a pressure medium is used toexpand or contract the bellows.